From a viewpoint of improving a yield in semiconductor fabrications, management of a surface condition in a bevel portion of a wafer has recently been receiving attention. In semiconductor device fabrication processes, a number of materials are deposited on an entire surface of a wafer. As a result, these materials are formed as films on a bevel portion which is not used for products. These unwanted materials may come off the bevel portion onto devices formed on the wafer during transporting of the wafer or during various processes, resulting in a lowered yield in products.
Thus, a polishing apparatus has been widely used to remove the films formed on the bevel portion of the wafer. A typical example of the polishing apparatus of this type is a polishing apparatus configured to press a polishing tape against the bevel portion of the wafer to polish the bevel portion. More specifically, the polishing apparatus has a press pad arranged at a rear side of the polishing tape and presses a polishing surface of the polishing tape against the bevel portion of the substrate by the press pad to thereby polish the bevel portion.
In recent years, a technique of detecting a polishing end point from an image of a surface of the bevel portion captured by an imaging device (e.g., a CCD camera) during polishing has been developed. In this technique, in order to accurately detect the polishing end point, it is necessary to capture as clear an image as possible. However, in a typical bevel polishing process, a polishing liquid (e.g., pure water) is supplied to the bevel portion during polishing in order to protect a surface of the wafer from contamination by particles. This polishing liquid is likely to adhere to an objective lens of the imaging device, making it difficult to capture a clear image of the bevel portion. As a result, accurate detection of the polishing end point cannot be performed.